Papers by Keyword: Crystallization Kinetics

Abstract: Poly (ethylene 2,5-furandicarboxylate) (PEF) is a bio-based polyester that is the subject of growing interest as a potential alternative to Poly (ethylene terephthalate) (PET) for sustainable packaging. Its excellent gas-barrier properties and reduced carbon footprint make it a promising candidate, but its use at industrial scale requires a solid understanding of how temperature and thermal history affect its mechanical and viscoelastic behavior. In this study, Differential Scanning Calorimetry (DSC), Dynamic Mechanical Thermal Analysis (DMA), and optical microscopy were used to characterize the thermal transitions and crystallization behavior of PEF, compared with PET and recycled PET (rPET). DSC results show that thermal crystallization of PEF proceeds very slowly, a result confirmed by in-situ microscopy. DMA measurements provide complementary information on the evolution of both storage and loss moduli with temperature, highlighting its dependence on crystallinity and thermal history. Together, these thermal and mechanical analyses clarify how PEF’s crystallization behavior affects its thermo-mechanical response. From a processing perspective, the very slow thermal crystallization of PEF is advantageous for stretch blow molding (SBM) process of bottles, as the polymer remains essentially amorphous during heating and crystallizes predominantly under deformation during the fast forming stage.

Abstract: Low temperature sintered MgO-Al₂O₃-SiO₂ glass-ceramic with high mechanical and low thermal expansion was prepared for package. The remarkable influence of B₂O₃ addition on the electrical, mechanical, and thermal properties was fully investigated. A small amount of B₂O₃ promoted the sintering process and improved the densification of MAS. The kinetics via Kissinger method indicated that an appropriate B₂O₃ content decreased the activation energy and helped the occurrence of crystallization. Due to the increase of crystallinity and indialite phase, B₂O₃ addition significantly enhanced flexural strength and Young’s modulus. MAS doped with 3wt% B₂O₃ can be sintered at 900 °C and obtained good properties: σ = 229 MPa, φ = 86 GPa, α = 1.66×10^-6 /°C, ε_r = 5.29, and tanδ = 5.9×10^-4.

Abstract: The aim of the presented work is an effort to answer the research questions, i.e. how to determine the optimal supersaturation temperature for multicomponent alloys What is the relationship between changes in the derivative curve of composites and the relationship between their chemical composition and microstructure Searching for the right answer to the above questions was the basis for determining the scope and methodology of the presented work. To describe the phenomena that occur in the material during solidification under various conditions caused by the variable cooling rate and variable chemical composition it was decided to use thermal-derivative analysis methods. The mentioned method allows to accurately describe and interpret the kinetics of the crystallization of the tested materials. This method is often used in the search for new directions of modern technologies, attractive from both experimental and cognitive. This methodology allows to determine the relationship between crystallization kinetics and usable casting properties on the example of Al-Si-Cu alloys and other alloying elements.

Abstract: Isothermal crystallization kinetics and morphology of Poly (lactic acid) (PLA) and PLA/ethylene acrylate copolymer (EAC) blends were studied by differential scanning calorimetry (DSC) and polarized optical microscopy (POM) at various temperatures (95–125°C). The DSC data obtained was analyzed using the Avrami equation. The crystallization rate was found to depend on the crystallization temperature (T_c) and EAC content. At a given T_c, the crystallization rate value was greater in the blends than in PLA suggesting that the presence of EAC enhanced crystallization of PLA. Based on the DSC analysis the crystallization rate was maximum when PLA blend with 1 wt.% EAC was isothermally crystallized at 103°C. The presence of EAC did not significantly change in the spherulitic growth rate (G) of PLA. Analysis of the growth rates using the Lauritzen-Hoffman theory showed that a regime II to regime III transition was present for all PLA/EAC blends and that this transition occurred at temperature of 100°C. The fold surface energy values of PLA/EAC blends were lower than that of PLA indicating that PLA chains can readily fold onto the crystal nucleus surface after the incorporation of EAC.

Abstract: The influence of molecular weight of poly (D-lactide) (PDL) on the melt crystallization was successfully investigated by non-isothermal differential scanning calorimetry (DSC) technique. The synthesized PDLs with three different number average molecular weights (Mn) of 2.39×10⁵ (PDL1), 1.09×10⁵ (PDL2) and 0.61×10⁵ (PDL3) were utilized in this study. From DSC kinetics analysis, it was found that the rate of PDLs crystallization increased with increasing cooling rate. Furthermore, the crystallization rate of PDLs was dependent on molecular weight and determined to be in the following order: PDL3 > PDL2 > PDL1. The crystallization mechanism was analyzed by the Avrami, Ozawa and Liu models. The mechanism of all PDLs crystallization was nucleation with three dimensional growths. Furthermore, the molecular weight of PDLs affected not only the crystallization rate but also the thermal property. As the molecular weight of PDLs increased, the melting temperature (T_m) increased but the heat of melting (∆H_m) decreased.

Abstract: The crystallization kinetics of melt-spun Cu_64.5Zr_35.5 amorphous alloy ribbons was investigated using differential scanning calorimetry (DSC) at different heating rates. Besides, the Kissinger and isoconversional approaches were used to obtain the crystallization kinetic parameters. As shown in the results, the activation energies for glass transition and crystallization process at the onset, peak and end crystallization temperatures were obtained by means of Kissinger equation to be 577.65 ± 34, 539.86 ± 54, 518.25 ± 20 and 224.84 ± 2 kJ/mol, respectively. The nucleation activation energy E_nucleation is greater than grain growth activation energy E_growth, indicating that the nucleation process is harder than grain growth. The local activation energy E_α decreases in the whole crystallization process, which suggests that crystallization process is increasingly easy.

Abstract: PP/EPDM blends were prepared by dynamic vulcanization technology within a HAAKE torque rheometer. The effect of different plastic/rubber ratios of PP/EPDM blends on the curing behavior and crystallization kinetics were investigated. The obtained results showed that the plastic/rubber ratios played an important part in the solidification process as well as the crystallization kinetics. With increasing EPDM content, the cooling rate of PP/EPDM blends was significantly larger than that of neat PP. When PP content was 20 wt%, the crystallinity of PP was obviously larger than that of neat PP. Compared with neat PP, the crystallization temperature of the blends were remarkably shifted to the lower temperature. EPDM particles showed active effect on the nucleation process of PP during the cooling crystallization of the PP/EPDM blends.

Abstract: The glass-ceramics were produced via heat treatment from bulk base glass at the appropriate treatment temperatures provided by the differential thermal analysis (DTA) measurement. The effect of nucleation on crystallization kinetics has been explored. It is found that nucleation indeed decreased the activation energy of crystallization. X-ray diffraction (XRD) analysis demonstrated that the main crystalline phase was magnesium alumino-silicate (MgAl₂Si₃O₁₀), Scanning electron microscopy (SEM) morphology showed that the crystals were needle-like in all the samples.

Abstract: Crystallization kinetics experiment of calcium sulfate dehydrates, which is prepared by bittern under 40oC and 200r/min conditions, is carried out. According to the results of the experimental data, the relationship of nucleus particle-number density n⁰ and crystal growth rate G with the residence time is summarized. Also, the average diameter of gypsum crystal is decreasing with the residence time increase. Meanwhile, the crystallization kinetics formula is derived to be: B⁰=3.20×10⁵G^0.47.

Abstract: Glass forming ability and crystallization kinetics of Al-Mg-Ni-La alloys have been investigated by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The maximum thickness achievable in glasses of Al₇₆Mg₁₁Ni₈La₅ and Al₆₉Mg₁₈Ni₈La₅ ribbons were 200 and 120 μm, respectively. The crystallization temperature and peak temperature indicated by DSC measurements displayed dependence on the heating rate during continuous heating, and were coincident with Lanoka’s relationship. The activation energies for the crystallization reaction E_x were obtained from the Kissinger’s equation. The results show the Mg addition is beneficial to the thermal stability of the amorphous phase.